Development of Simultaneous Removal System for Radioactively Gaseous and Particulate Matters generated by Dismantlement of Nuclear Power Plants

本工作的目的是开发一个同时去除系统的气体和颗粒物质产生的热切割的活化钢结构在老化的核电厂拆除。本论文主要研究了八羰基二钴（octacarbonyl di-cobalt，OCDC）在钢结构热切割过程中的气相行为。OCDC蒸气通过用己烷制备的OCDC溶液的雾化，然后过滤形成的雾来产生。然后，我们测量了它的分解速率在不同的停留时间，其蒸气浓度和温度的基础上的假设，该反应是连续的一级反应，通过一个中间体。结果发现，分解成中间体的前一过程主导这些反应。此外，我们估计了生成的颗粒的尺寸，考虑到分解管作为扩散管来调节反应的停留时间，并且获得了估计的尺寸至少大于1 nm。这些发现表明，我们需要形成的OCDC蒸气的停留时间超过20秒，并且周围温度略高于房间温度，以便将其转化为颗粒，随后用HEPA过滤器将其去除。

The present work is aimed at developing a simultaneous removal system for gaseous and particulate matters generated by thermal cutting of activated steel constructions during the dismantlement of aged nuclear power plants. In the present work, we focused on octacarbonyl di-cobalt(OCDC), which belongs to cobalt-compounds with high radioactivity during the thermal cutting of steel constructions, and investigated its behaviors in gas phase. OCDC vapor was generated by atomization of OCDC-solution prepared with hexane followed by filtration of the formed mists. Then, we measured its decomposition rates at various residence times, its vapor concentrations and temperatures based on the assumption that this reaction is consecutive first-order reactions via an intermediate. As a result, it was found that the former process of decomposition into the intermediate dominates these reactions. Also, we estimated the size of generated particles, considering the decomposition tube to adjust the residence time for reaction as a diffusion tube, and obtained that the size was estimated to be at least larger than 1 nm. These findings suggested that we need the residence time of formed OCDC vapor more than 20s and the surrounding temperature somewhat higher than room one in order to convert it into particles and subsequently remove them with HEPA filters.